Selecting circuits



Aug. '17 1925. 1,596,087

L. ESPENSCHIED I SELECTING CIRCUITS Filed Dec. 30, 1921 1m we flaL/VSakh 2 SheetsShe6t 1 '76 VZ'Sender of lewa'wr INVENTOR ATTORNEY Aug. 17 1926. 1,596,087

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INVENTOR L 6 ATTORNEY Patented Aug, 17, 1926.

v, UNITED "STATES PATENT OFFICE.

' LLOYD ESPEHSCHIED, O13 QUEENS, NEW YORK, ASSIGNOB TO AMERICAN TELEPEONI AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

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Application filed December 80, 1921. Serial R0. 635,897.

This invention relates to signaling circuits and more particularly to a form of selective terminal clrcuit adapted to permit of superposing alternating current of carrier current 8 channels upon ordinary telephone and telegraph circuits.

- ()ne of the objects of the present 1I1VEfition is to provide a low frequency carrier channel employing frequencies of the order of 100 to 300 cycles per second, althou h the invention is equally a plicable to hig fre quency transmission. guch a channel may be used for any signaling purpose as, for 'ex- I ample, telegrap1 i nahng in whic the signaling frequency is low relative to 'the carrler frequency.

In carrying out the objects of this invention the carrier channel is balanced inmultiple with other channel terminals, such as telephone and direct current telegraph channels, for the purpose of avoidin interference between the. oppositely irected transmissions of the different channels. It

is also proposed to use sharply tuned selective circuits for the terminal frequency selective circuits of the terminals frequency se- I lecting system and preferably a capacitive type of loose coupling will be employed between the individual sharply tuned circuits.

so The capacitive type of coupling, has an important advantage over the inductive coup-.

' ling in that it tends suppress the transmission of the harmonics of the carrier frequency which would otherwise tend to inter- .88 fere with the channels operatingon higher frequencies, particularly with the telephone channel, the frequency band of which embraces a number of harmonics of the lower frequency of the carrier which it ferred to use in connection with the type of channel forming the subject matter of the present invention.

The invention may now be more fully understood from the following description as when read in connection with the accompanying drawing, Figures 1, 2 and 3 of which show different types of selecting circuits embodying the principles of the present invention, Figs. 4 and 5 of which illustrate to circuit arrangements for signaling systems employing the selective circuits shown in Figs. 1, 2- and 3, while Figs. 6, 7 and 8 illus trate difierent arrangements for associating or telephone control s1g-' ties of the condensers C and C are and their sole purpose 1s is pre- I loosely coupled b the transmitting and receiving apparatus with the circuit of Fig. 5.

Referring to Figs. 1, 2 and 3, three or more circuits may be coupled together either individualiy or in common. For example, let us suppose we have a selecting system comprising a tuned circuit for the line connection oi? the system, a tuned circuit for the baiancing connection of the system, and a third tuned circuit associated with the drop,

that is, the transmitting or receiving apparatus. in such a system as'shown in Fi 1 the iine tuned circuit land the networ tuned. circuit 2 are coupled individually through coupling condensers C and C respectively to the drop side tuned circuit 3. Each of the three tuned circuits iseiectricall similar, the tuning being determined y suitable inductances and capacities in a well known manner. The capaciuite large as compared with the capacities o? the tuning condensers in the circuits 1, 2 and 3,

coupling between The coupling condensers are bridged across the circuit and, owing to their large capacity, form aths of practically negligible imped to provide a loose the individual circuits.

ance or high frequencies so that if a generator is associat with the tuned circuit 3 for example, the harmonics of the generator will not be transmitted .beyond the condensers 0,, and C,,, as these condensers will practically short-circuit the apparatus beyond the condensers so far as the flow of the higher frequencies is concerned. In associating a transmitter or a receiver with the tuned circuit 3, for example, the connection may be made across ferent potential. In the case-illustrated, the connection is made to opposite terminals of the tuning condenser of the circuit 3.

Fig. 2 illustrates an arrangement for coupling the three circuits in common. this case, the tuned circuits 1 and 2 are 2. ca acitive coupling comprising a con enser similar in its function to the condensers C or 0,, already described. A third tuned circuit 3 to be associated with the drop, for example, may be connected to the terminals of the couplin condenser C in the same manner as iihecircuits 1 and 2, so that all three any two points of diftuned circuits are coupled together in pom- I oose' coup mg.-

. with the balancing circuit. This is for the reason that the tuned circuit 3 is in effect ridged across the other'two tuned circuits and willform a neutral connection with respect to. a receiving circuit where one is employed, as will hedescrihed later.

Fig-3 shows an arrangement in which 7 the tuned circuitsl and 2are loosely coupled i togetherthrough a condenser th rd C and the tuned circuit 4 is loosely coupled to the tunedcircuits 1 and 2 through an inductive'cou ling partaking of the nature of a hyiuricl coil 10. This inductive type of coupling is suitable where the circuit is to be employed for receiving, in which case monies. sociated, for example, of the tuned circuit 4..

how a selectin I the network N.

- tionally illustrated atv conjugate with respect to each to guard against harit is not necessary m llhe recelving circuit may be as- Fig. 4 shows an arrangement illustrating circuit of the type shown v in Fig. 1 may -be employed for two-way operation. Two channels TL and RL may be connected in multiple to the line connection EA and to, the halancing network N. Each channel includes three tuned cir- Y cults coupled its-illustrated in Fig. 1. The sh transmitting apparatus '1, which may be. ot any type, is connected to opposite ter-' minals o the tuning condenser of thecircuit-3 and the receivinapparatus, convennected across the tuning condenser of the circuit 3. The two channels may he made other for similar connections of the transmitting and receiving apparatus to the individual channels by reversing the connections of one of the channels, the channelRL, where it is connected to 2 and 3 may be orm a two-way cir- The circuits of Fi readily combined to cuit as illustrated in Fig. 5. The tuned circuits 3., 2 and 3 are loosely coupled in common through the cou ling condenser the hybrid coil arrangement v the circuits 1 i cuit t through ,obvious' that the transmitter and receiver will be conjugate with respect "to each other and the channel including the circuits 1 and 1 C and the transmitting evic-e T is connected to the tuned circuit 3. A fourth tuned circuit l is inductively cou led by and 2 and the paratus R is connected to the tune cira' transformer 5. It will he 2 may he bridged to the line L and the network N in parallel with other channels for --used, such, for example,

with the terminalsreceiver being 1s similarly con-W on the other hand,

as shown in connection with of Fig. 3 to i receivin ap-.

emplo ing other carrier frequencies or employe for ordinary telephone or direct current telegraph transmission.

Where the transmitter. T is a high ime pedance' device, as will-be the case when the transmitting alpparatus includes a vacd be connected in Similarly, the receiving device R, where parallel with the tuning element of the oil by connecting it it is of high impedance, is associated with the tuned circuit 4 through the transformer 5.' Where a low impedance transmitter is it may be included serially in the tuned circuit 3 as illustrated in Fi .8. LA low impedance receiver may also in series with the tuned circuit 4 'as illustrated in Fig. 6, the apparatus of which may re lace the apparatus abovethe terminals and 8 in Fig. 7 shows an alternative arrangement for connecting a high impedance-receiver, the

connected in tuning condenser of the tuned circuit 4 and the apparatus of Fig. 7 being likewise in tended to replace the apparatus of Fig, 5 above theterminals 7 and'8. 1 .71

-.Where "the transmitting and receiving apparatus are coupled together by means of a conjugate arran own in\Fig. 5, it. is, of course, necessary to use the same frequency for transmitting and receiving'as allof the circuits and 4 mustbe tuned to, the same frequency. Theloose coupling between the several circuits is necessary in order to prevent the double peak effectof the frequency amplitude curve observedwhere tuned circuits are closely coupled. The arrangement of Figs, permits of the use of dif-v ferent frequencies for transmitting and re ceiving, as the three tuned circuits in'the channel TL maybe/tuned to difi'erent it'requencies from those in the channel RL', ow-

ing to the fact that the two sets of tuned circuits are not coupled together. The three tuned circuits in a given channel as, for example, in the transmitting channel, will of course, he tuned to the same frequency.

v g It will be obvious that the general ciples herein disclosed may be embodied in many other organizations widely dig er-sent from those illustrated with'out departin in the following claims.

What is claimed is: l g 1. In a selective systemya transmission path and ahalancing path, circuits in emh Bath tuned to the same frequency; and so oosely coupled together as to ently resonant, a third tuned circuit coupled to each of the othertuned circuits, and a connected an alternator,

35 the circuit of Fig. 5., I

O0 parallel with the gement such as that 3 prinv lee i cm the spirit of the invention as defin ies be iildependa means? other tuned circuits, an a transmitting device associated with the third tuned circuit. 3. In a selective system, a pair of'tuned circuits loosely coupled to ether, a third tuned circuit loosely couple toeach of the first two tuned circuits in the same manner, and a fourth tuned circuit cou led to-each of the first two tuned circuits through connections which are similar to each other, the coupling for the third. and fourth tuned circuits being so arranged and fourth circuits, will be conjugate with respect to each other.

4. In a selective system, a pair of tuned circuits looselycoupled together through a capacitive cou lin a third tuned circuit coupled to eac oi the first two tuned circuits through the same capacitive coupling, and a fourth tuned circuit loosely coupled to the first'and second tuned circuits, said last mentioned coupling being so arranged that said third and fourth circuits will be conjugate.

5. In a selective system. a'pair of tuned circuits having common terminals, a third tuned circuit also connected to said common terminals, a capacitive loose coupling bridged across said common terminals for loosely coupling the three tuned circuits together, a fourth tuned circuit inductively coupledto said first and second circuits through windings arranged on each side of that said third 7 said common terminals, whereby said it and fourth circuits will be substantir conjugate.

6. Ina selective system, a transmission path, a balancing path, a tuned circuit in each path, a capacitive coupling for loosely coupling the two tuned circuits, transmit ting apparatus, a third tuned circuit as sociated therewith, said third tuned circuit being loosely coupled to the first and. sec ond tuned circuits through said common capacitive coupling, a receiving apparatus, a fourth tuned circuit associated therewith, said fourth tuned circuit being loosely coupled to the tuned circuits in said trans mission path and balancing path manner as to be conjugate with its i said third tuned circuit.

7 ..In a selective system, a transmission path, a balancing path, tuned circuits in each of said paths, said tune-dv circa ing common terminals, a transmitt apparatus including a tuned circmc, .tuned a, circuit also being connected to said common terminals, a capacity bridged across said terminals for loosely coupling the three tunedcircuits together, a receiv mg apparatus including afourth tuned circuit, said fourth tuned circuit being in ductively coupled to the tuned circuits n said transmisison path and said balancing path through windings on either side of said common terminals whereby the trans mitting and receiving apparatus will be r substantially conjugate.

In testimony whereof, I have signed my name to this specification this 29th day of -December 1921.

.: r LLOYD ESPENSGHIED. 

